Normally closed fluid control devices are already known which comprise a valve case having a fluid channel, a valve element holder upwardly or downwardly movable for holding a valve element for opening or closing the fluid channel, a lower casing attached to a bonnet provided on an upper portion of the valve case, an upper casing joined to the lower casing, a valve stem disposed in a space defined by the upper and lower casings and having a lower end in bearing contact with the valve element holder, a piston secured to the valve stem by a retaining ring, and a compression coil spring bearing on and retained by the top wall of the bonnet and a flange provided on the valve stem so as to be positioned below the bonnet top wall. The fluid channel is opened by admitting compressed air into a lower space formed between and defined by the lower surface of the piston and the upper surface of bottom wall of the lower casing (see, for example, the publication of JP-A No. 11-256578, pars. 0002 to 0003 and FIG. 3).
The normally closed fluid control device may be modified into a normally open fluid control device by providing a compression coil spring as held between a lower portion of a bonnet and a flange provided on the valve stem so as to be positioned above the bonnet lower portion and introducing compressed air into an upper space formed between and defined by the upper surface of the piston and the lower surface of top wall of the upper casing.
With the conventional fluid control devices described above, the normally closed type and the normally open type are handled as different individual devices, such that when designing one of these two types, no consideration is given to the interior construction of the other type. Accordingly, the control device of the normally open type and that of the normally closed type as used on the same piping system are very great in the combined number of components.
An object of the present invention is to provide a fluid control device which is useful for providing fluid control devices of the normally closed type and the normally open type which are reduced in the combined number of components.